Texas Instruments presently manufactures torsional dual axis and single axis mirror MEMS devices fabricated out of a single piece of material (such as silicon, for example) typically having a thickness of about 100–115 microns. Although manufacturing has been substantially limited to mirrors, it will be appreciated that the use of such torsional hinges may be equally applicable to other functional surface such as light grates or even devices not related to light or light beams. The dual axis layout consists of a functional surface or mirror normally to light or light beams. The dual axis layout consists of a functional surface or mirror normally supported on a gimbal frame by two silicon torsional hinges, whereas for a single axis device the surface mirror is supported directly by a pair of torsional hinges. The gimbal frame used by the dual axis device is attached to a support frame by another set of torsional hinges. One example of a dual axis torsional hinged mirror is disclosed in U.S. Pat. No. 6,295,154 entitled “Optical Switching Apparatus” and was assigned to the same assignee on the present invention.
According to the prior art, torsional hinge devices were initially driven directly by magnetic coils interacting with small magnets mounted on the pivoting surface at a location orthogonal to and away from the pivoting axis to oscillate the device or, in the case of a mirror, create the sweeping movement of the beam. In a similar manner, orthogonal movement of the device was also controlled by magnetic coils interacting with magnets mounted on the gimbals frame at a location orthogonal to the axis used to pivot the gimbals frame.
According to the earlier prior art, the magnetic coils controlling the functional surface portion (such as a mirror) typically received a positive or negative signal to position and hold the device at a precise rotational angle. Little or no consideration was given to the resonant pivoting frequency of the device, and in the application to mirrors, most of the earlier optical switching mirrors had a resonant frequency of around 100 Hz. Consequently, not only was the pivoting speed of the device rather slow, but also significant energy could be required to pivot the functional surface. Furthermore, the magnets mounted on the functional surface portion added mass and limited the pivoting speed.
Therefore, a dependable and inexpensive drive mechanism to rapidly position and maintain a torsional device at a precise angular rotation would be advantageous.